Heat emitting plates are presently extensively used as head radiating sources. Their wide use and acceptance can be attributed to their relatively small size, high heating efficiency, and low manufacturing costs, the latter resulting from the fact that the materials are inexpensive and the manufacturing process per se is quite simple. Other advantages of heat emitting plates reside in their versatility and capability of being readily adapted to a variety of heating uses, features which render them capable of solving a wide variety of practical heating problems.
Generally, heating plates, when positioned for use, are placed in an upright position. When so positioned, however, convection causes the heat radiated by the lower part of the plate to heat the upper part of the plate. This effect results in a marked difference of thermal energy throughout the plate since the lower part of the plate is able to reach the optimum temperature while this optimum temperature is exceeded in the upper part of the plate. This heat differential across the plate results in expansion and stress, both in the plate and in the supporting structure.